Nearly 47 million individuals speak languages other than English in the United States. However, patterns of typical and atypical language development in bilingual children remain unclear, and the ability to construct valid and reliable bilingual assessment tools is therefore limited. Since early diagnosis of a speech-language impairment is instrumental to successful intervention, and ultimately, to the child's quality of life, the lack of assessment tools appropriate for use with bilingual children constitutes a significant health risk. The long-term goal of this research is to develop theoretically-grounded assessment methods appropriate for use with bilingual children along a wide range of proficiency levels. The goal of the present work is to use the theoretical framework of working memory to examine whether and how word-learning tasks index vocabulary knowledge in sequential bilingual children. Experiment 1 will compare Spanish-English sequential-bilingual and monolingual children ages 5-6 on their ability to learn phonologically-familiar novel words that follow the English phonological structure. It is hypothesized that knowledge of English vocabulary will influence children's performance on the phonologically-familiar word-learning task. Because sequential bilinguals have weaker vocabulary in English (their second language) compared to native speakers of English, it is predicted that monolingual children will outperform sequential-bilingual children on the phonologically-familiar task. Experiment 2 will compare Spanish-English sequential-bilingual and monolingual children on their ability to learn phonologically-unfamiliar novel words that do not follow either the English or the Spanish phonological structure. Knowledge of English vocabulary is hypothesized to have limited effect on encoding of phonologically-unfamiliar novel words. Therefore, it is predicted that sequential bilinguals and monolinguals will demonstrate comparable performance levels on the phonologically-unfamiliar task. The relationship between vocabulary skills and word-learning performance in bilingual vs. monolingual children will also be examined. If word-learning tasks are found to index bilingual children's conceptual rather than English-specific vocabulary knowledge, diagnostic use of word-learning tasks with bilingual children can be supported. If the phonologically-unfamiliar task yields comparable performance levels in bilingual and monolingual children, its use can be generalized to other bilingual children with different language-learning histories and proficiency profiles. Theoretically, the experiments will test the ability of the working memory model to accommodate and predict the association between vocabulary knowledge and phonological memory capacity in monolingual compared to bilingual children. PUBLIC HEALTH RELEVANCE: The current project aims to improve diagnostic practices with children who speak English as a second language, and who therefore cannot be tested using tools developed for monolingual English-speaking children. In the proposed work, we test whether word-learning tasks can serve as markers of typical vocabulary development in Spanish-speaking bilingual children who are acquiring English as a second language. Because early diagnosis of a language difficulty is key to successful intervention and to the child's ultimate quality of life, identification of tasks that can accurately index bilingual children's typical vs. atypical development can make significant contribution to public health.